[PATCH] drm/i915/skl: implement DP Aux Mutex framework

[PATCH] drm/i915/skl: implement DP Aux Mutex framework

[Wayne Boyer]

Beginning with SKL the DP Aux channel communication can be protected
using a built in H/W mutex.

This patch provides an initial implementation for using that mutex.
The use is currently limited to protecting the sink crc request based
on feedback from the H/W designers indicating that using the mutex
for all aux channel communication is not recommended.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/i915_reg.h |  5 ++++
 drivers/gpu/drm/i915/intel_dp.c | 52 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b12594b..98e991d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2604,6 +2604,7 @@ struct drm_i915_cmd_table {
 
 #define HAS_DDI(dev)		(INTEL_INFO(dev)->has_ddi)
 #define HAS_FPGA_DBG_UNCLAIMED(dev)	(INTEL_INFO(dev)->has_fpga_dbg)
+#define HAS_AUX_MUTEX(dev)	(INTEL_INFO(dev)->gen >= 9)
 #define HAS_PSR(dev)		(IS_HASWELL(dev) || IS_BROADWELL(dev) || \
 				 IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev) || \
 				 IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 8942532..a033e70 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4288,6 +4288,11 @@ enum skl_disp_power_wells {
 #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
 #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
 
+#define DP_AUX_MUTEX_A			0x6402C
+#define DP_AUX_MUTEX_B			0x6412C
+#define   DP_AUX_MUTEX_ENABLE		    (1 << 31)
+#define   DP_AUX_MUTEX_STATUS		    (1 << 30)
+
 /*
  * Computing GMCH M and N values for the Display Port link
  *
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2fad873..e9e1239 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -781,6 +781,47 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp *intel_dp,
 	       DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
 }
 
+static bool skl_aux_mutex(struct intel_dp *intel_dp, bool get)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_device *dev = intel_dig_port->base.base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t aux_ch_mutex, status;
+	int count = 0;
+
+	if (!HAS_AUX_MUTEX(dev))
+		return false;
+
+	/*
+	 * FIXME: determine actual aux channel
+	 * Hard coded to channel A for now to protect sink crc requests on eDP.
+	 */
+	aux_ch_mutex = DP_AUX_MUTEX_A;
+
+	if (!get) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE | DP_AUX_MUTEX_STATUS);
+		return false;
+	}
+
+	/*
+	 * The Bspec specifies waiting 500us between attempts to acquire the
+	 * mutex.  Ten retries should be adequate to balance successfully
+	 * acquirng the mutex and spending too much time trying.
+	 */
+	while (count++ < 10) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE);
+		status = I915_READ(aux_ch_mutex);
+		if (!(status & DP_AUX_MUTEX_STATUS))
+			return true;
+		udelay(500);
+	}
+
+	return false;
+}
+
+#define skl_aux_mutex_get(dev) skl_aux_mutex(dev, true)
+#define skl_aux_mutex_put(dev) skl_aux_mutex(dev, false)
+
 static int
 intel_dp_aux_ch(struct intel_dp *intel_dp,
 		const uint8_t *send, int send_bytes,
@@ -4188,10 +4229,14 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 	u8 buf;
 	int count, ret;
 	int attempts = 6;
+	bool aux_mutex_acquired = false;
+
+	aux_mutex_acquired = skl_aux_mutex_get(intel_dp);
 
 	ret = intel_dp_sink_crc_start(intel_dp);
+
 	if (ret)
-		return ret;
+		goto release;
 
 	do {
 		intel_wait_for_vblank(dev, intel_crtc->pipe);
@@ -4218,6 +4263,11 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 
 stop:
 	intel_dp_sink_crc_stop(intel_dp);
+
+release:
+	if (aux_mutex_acquired)
+		aux_mutex_acquired = skl_aux_mutex_put(intel_dp);
+
 	return ret;
 }
 
-- 
1.9.1

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Re: [PATCH] drm/i915/skl: implement DP Aux Mutex framework

[Jani Nikula]

On Tue, 10 Nov 2015, Wayne Boyer <wayne.boyer@intel.com> wrote:
> Beginning with SKL the DP Aux channel communication can be protected
> using a built in H/W mutex.
>
> This patch provides an initial implementation for using that mutex.
> The use is currently limited to protecting the sink crc request based
> on feedback from the H/W designers indicating that using the mutex
> for all aux channel communication is not recommended.

Please explain in the commit message what benefits this brings, and why
it's a good idea. Just that something *can* be done in hardware does not
mean that we should do it.

BR,
Jani.


>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  1 +
>  drivers/gpu/drm/i915/i915_reg.h |  5 ++++
>  drivers/gpu/drm/i915/intel_dp.c | 52 ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index b12594b..98e991d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2604,6 +2604,7 @@ struct drm_i915_cmd_table {
>  
>  #define HAS_DDI(dev)		(INTEL_INFO(dev)->has_ddi)
>  #define HAS_FPGA_DBG_UNCLAIMED(dev)	(INTEL_INFO(dev)->has_fpga_dbg)
> +#define HAS_AUX_MUTEX(dev)	(INTEL_INFO(dev)->gen >= 9)
>  #define HAS_PSR(dev)		(IS_HASWELL(dev) || IS_BROADWELL(dev) || \
>  				 IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev) || \
>  				 IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 8942532..a033e70 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4288,6 +4288,11 @@ enum skl_disp_power_wells {
>  #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
>  #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
>  
> +#define DP_AUX_MUTEX_A			0x6402C
> +#define DP_AUX_MUTEX_B			0x6412C
> +#define   DP_AUX_MUTEX_ENABLE		    (1 << 31)
> +#define   DP_AUX_MUTEX_STATUS		    (1 << 30)
> +
>  /*
>   * Computing GMCH M and N values for the Display Port link
>   *
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 2fad873..e9e1239 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -781,6 +781,47 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp *intel_dp,
>  	       DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
>  }
>  
> +static bool skl_aux_mutex(struct intel_dp *intel_dp, bool get)
> +{
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct drm_device *dev = intel_dig_port->base.base.dev;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	uint32_t aux_ch_mutex, status;
> +	int count = 0;
> +
> +	if (!HAS_AUX_MUTEX(dev))
> +		return false;
> +
> +	/*
> +	 * FIXME: determine actual aux channel
> +	 * Hard coded to channel A for now to protect sink crc requests on eDP.
> +	 */
> +	aux_ch_mutex = DP_AUX_MUTEX_A;
> +
> +	if (!get) {
> +		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE | DP_AUX_MUTEX_STATUS);
> +		return false;
> +	}
> +
> +	/*
> +	 * The Bspec specifies waiting 500us between attempts to acquire the
> +	 * mutex.  Ten retries should be adequate to balance successfully
> +	 * acquirng the mutex and spending too much time trying.
> +	 */
> +	while (count++ < 10) {
> +		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE);
> +		status = I915_READ(aux_ch_mutex);
> +		if (!(status & DP_AUX_MUTEX_STATUS))
> +			return true;
> +		udelay(500);
> +	}
> +
> +	return false;
> +}
> +
> +#define skl_aux_mutex_get(dev) skl_aux_mutex(dev, true)
> +#define skl_aux_mutex_put(dev) skl_aux_mutex(dev, false)
> +
>  static int
>  intel_dp_aux_ch(struct intel_dp *intel_dp,
>  		const uint8_t *send, int send_bytes,
> @@ -4188,10 +4229,14 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  	u8 buf;
>  	int count, ret;
>  	int attempts = 6;
> +	bool aux_mutex_acquired = false;
> +
> +	aux_mutex_acquired = skl_aux_mutex_get(intel_dp);
>  
>  	ret = intel_dp_sink_crc_start(intel_dp);
> +
>  	if (ret)
> -		return ret;
> +		goto release;
>  
>  	do {
>  		intel_wait_for_vblank(dev, intel_crtc->pipe);
> @@ -4218,6 +4263,11 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  
>  stop:
>  	intel_dp_sink_crc_stop(intel_dp);
> +
> +release:
> +	if (aux_mutex_acquired)
> +		aux_mutex_acquired = skl_aux_mutex_put(intel_dp);
> +
>  	return ret;
>  }

-- 
Jani Nikula, Intel Open Source Technology Center
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Re: [PATCH] drm/i915/skl: implement DP Aux Mutex framework

[Dave Airlie]

On 10 November 2015 at 20:51, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Tue, 10 Nov 2015, Wayne Boyer <wayne.boyer@intel.com> wrote:
>> Beginning with SKL the DP Aux channel communication can be protected
>> using a built in H/W mutex.
>>
>> This patch provides an initial implementation for using that mutex.
>> The use is currently limited to protecting the sink crc request based
>> on feedback from the H/W designers indicating that using the mutex
>> for all aux channel communication is not recommended.
>
> Please explain in the commit message what benefits this brings, and why
> it's a good idea. Just that something *can* be done in hardware does not
> mean that we should do it.

I also have trouble understanding a mutex that only some things use. Seems
like a mutex needs to be used everywhere to provide locking.


Dave.
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Re: [PATCH] drm/i915/skl: implement DP Aux Mutex framework

[Vivi, Rodrigo]

When PSR is enablabled the Hardware takes control on AUX and use it to
control panel exit/entry states.

When validating PSR with automated tests grabbing CRC from sink we were
facing strange aux communication issues where aux were returning
message size read equal 0. And 0 is a forbidden message.

So, by using the HW mutex you block HW from using aux when we are going
to use here on the automated PSR tests.

There was a bug opened at fd.o regarding sink_crc failing on SKL when
PSR was enabled but I couldn't find it. But we have 3 different
solutions for this case where we are trying to read sink crc and aux
being used by Hardware:

1. Use intel_dp_dpcd_read_wake for all dpcd reads at sink_crc. 

2. Return -EBUSY when message size is zeroed so drm takes care of
reties.

3. Use HW mutex so we let HW know we are going to use the aux.


Either one is fine for me as long as we have a reliable sink crc on SKL
and KBL.

Well, regarding this patch itself it seems that maintainers would need
a better description, but for the content I'm sure it is right and I
tested it here so feel free to use:

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>


On Tue, 2015-11-10 at 21:14 +1000, Dave Airlie wrote:
> On 10 November 2015 at 20:51, Jani Nikula <
> jani.nikula@linux.intel.com> wrote:
> > On Tue, 10 Nov 2015, Wayne Boyer <wayne.boyer@intel.com> wrote:
> > > Beginning with SKL the DP Aux channel communication can be 
> > > protected
> > > using a built in H/W mutex.
> > > 
> > > This patch provides an initial implementation for using that 
> > > mutex.
> > > The use is currently limited to protecting the sink crc request 
> > > based
> > > on feedback from the H/W designers indicating that using the 
> > > mutex
> > > for all aux channel communication is not recommended.
> > 
> > Please explain in the commit message what benefits this brings, and 
> > why
> > it's a good idea. Just that something *can* be done in hardware 
> > does not
> > mean that we should do it.
> 
> I also have trouble understanding a mutex that only some things use. 
> Seems
> like a mutex needs to be used everywhere to provide locking.
> 
> 
> Dave.
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[PATCH] drm/i915/skl: implement DP Aux Mutex framework

[Wayne Boyer]

Beginning with SKL the DP Aux channel communication can be protected
using a built in HW mutex.

When PSR is enablabled the HW takes control on AUX and uses it to
control panel exit/entry states.

When validating PSR with automated tests, grabbing CRC from sink
revealed strange aux communication issues.  Aux reads were returning
a message read size equal to 0 and 0 is a forbidden message.

By using the HW mutex the HW is blocked from using aux when running
the automated PSR tests.

This patch provides an initial implementation for using that mutex.
The use is currently limited to protecting the sink crc request based
on feedback from the H/W designers indicating that using the mutex
for all aux channel communication is not recommended.

v2: Improved commit message to explain the case where the HW mutex is
helpful.  Also added bug reference.

Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91437
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/i915_reg.h |  5 ++++
 drivers/gpu/drm/i915/intel_dp.c | 52 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b12594b..98e991d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2604,6 +2604,7 @@ struct drm_i915_cmd_table {
 
 #define HAS_DDI(dev)		(INTEL_INFO(dev)->has_ddi)
 #define HAS_FPGA_DBG_UNCLAIMED(dev)	(INTEL_INFO(dev)->has_fpga_dbg)
+#define HAS_AUX_MUTEX(dev)	(INTEL_INFO(dev)->gen >= 9)
 #define HAS_PSR(dev)		(IS_HASWELL(dev) || IS_BROADWELL(dev) || \
 				 IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev) || \
 				 IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 8942532..a033e70 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4288,6 +4288,11 @@ enum skl_disp_power_wells {
 #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
 #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
 
+#define DP_AUX_MUTEX_A			0x6402C
+#define DP_AUX_MUTEX_B			0x6412C
+#define   DP_AUX_MUTEX_ENABLE		    (1 << 31)
+#define   DP_AUX_MUTEX_STATUS		    (1 << 30)
+
 /*
  * Computing GMCH M and N values for the Display Port link
  *
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2fad873..e9e1239 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -781,6 +781,47 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp *intel_dp,
 	       DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
 }
 
+static bool skl_aux_mutex(struct intel_dp *intel_dp, bool get)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_device *dev = intel_dig_port->base.base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t aux_ch_mutex, status;
+	int count = 0;
+
+	if (!HAS_AUX_MUTEX(dev))
+		return false;
+
+	/*
+	 * FIXME: determine actual aux channel
+	 * Hard coded to channel A for now to protect sink crc requests on eDP.
+	 */
+	aux_ch_mutex = DP_AUX_MUTEX_A;
+
+	if (!get) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE | DP_AUX_MUTEX_STATUS);
+		return false;
+	}
+
+	/*
+	 * The Bspec specifies waiting 500us between attempts to acquire the
+	 * mutex.  Ten retries should be adequate to balance successfully
+	 * acquirng the mutex and spending too much time trying.
+	 */
+	while (count++ < 10) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE);
+		status = I915_READ(aux_ch_mutex);
+		if (!(status & DP_AUX_MUTEX_STATUS))
+			return true;
+		udelay(500);
+	}
+
+	return false;
+}
+
+#define skl_aux_mutex_get(dev) skl_aux_mutex(dev, true)
+#define skl_aux_mutex_put(dev) skl_aux_mutex(dev, false)
+
 static int
 intel_dp_aux_ch(struct intel_dp *intel_dp,
 		const uint8_t *send, int send_bytes,
@@ -4188,10 +4229,14 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 	u8 buf;
 	int count, ret;
 	int attempts = 6;
+	bool aux_mutex_acquired = false;
+
+	aux_mutex_acquired = skl_aux_mutex_get(intel_dp);
 
 	ret = intel_dp_sink_crc_start(intel_dp);
+
 	if (ret)
-		return ret;
+		goto release;
 
 	do {
 		intel_wait_for_vblank(dev, intel_crtc->pipe);
@@ -4218,6 +4263,11 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 
 stop:
 	intel_dp_sink_crc_stop(intel_dp);
+
+release:
+	if (aux_mutex_acquired)
+		aux_mutex_acquired = skl_aux_mutex_put(intel_dp);
+
 	return ret;
 }
 
-- 
2.5.0

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Re: [PATCH] drm/i915/skl: Implement DP Aux Mutex framework

[Jani Nikula]

"aux mutex framework" in the title sounds a bit grandiose, to be
honest. "add support for DP AUX hardware mutex" is what I would have
used.

Further comments inline.

On Thu, 12 Nov 2015, Wayne Boyer <wayne.boyer@intel.com> wrote:
> From: "Boyer, Wayne" <wayne.boyer@intel.com>
>
> Beginning with SKL the DP Aux channel communication can be protected
> using a built in HW mutex.
>
> When PSR is enabled the HW takes control on AUX and uses it to
> control panel exit/entry states.
>
> When validating PSR with automated tests, grabbing CRC from sink
> revealed strange aux communication issues.  Aux reads were returning
> a message read size equal to 0 and 0 is a forbidden message.
>
> By using the HW mutex the HW is blocked from using aux when running
> the automated PSR tests.
>
> This patch provides an initial implementation for using that mutex.
> The use is currently limited to protecting the sink crc request based
> on feedback from the H/W designers indicating that using the mutex
> for all aux channel communication is not recommended.
>
> v2: Improved commit message to explain the case where the HW mutex is
> helpful.  Also added bug reference.
> v3: Fix typos in commit message.
>
> Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91437
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Tested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  1 +
>  drivers/gpu/drm/i915/i915_reg.h |  5 ++++
>  drivers/gpu/drm/i915/intel_dp.c | 52 ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index d5cf30b..ac7ed0d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2585,6 +2585,7 @@ struct drm_i915_cmd_table {
>  
>  #define HAS_DDI(dev)		(INTEL_INFO(dev)->has_ddi)
>  #define HAS_FPGA_DBG_UNCLAIMED(dev)	(INTEL_INFO(dev)->has_fpga_dbg)
> +#define HAS_AUX_MUTEX(dev)	(INTEL_INFO(dev)->gen >= 9)
>  #define HAS_PSR(dev)		(IS_HASWELL(dev) || IS_BROADWELL(dev) || \
>  				 IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev) || \
>  				 IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 8bd2699..f9ee874 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4288,6 +4288,11 @@ enum skl_disp_power_wells {
>  #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
>  #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
>  
> +#define DP_AUX_MUTEX_A			0x6402C
> +#define DP_AUX_MUTEX_B			0x6412C

Please add all of these at once, using an underscore prefix, and add
DP_AUX_MUTEX(port) to pick the right one. Plenty of examples in the
file. And then Ville doesn't have to clean it up afterwards.

> +#define   DP_AUX_MUTEX_ENABLE		    (1 << 31)
> +#define   DP_AUX_MUTEX_STATUS		    (1 << 30)
> +
>  /*
>   * Computing GMCH M and N values for the Display Port link
>   *
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index da02ed7..b3c7d82 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -781,6 +781,47 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp *intel_dp,
>  	       DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
>  }
>  
> +static bool skl_aux_mutex(struct intel_dp *intel_dp, bool get)
> +{
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct drm_device *dev = intel_dig_port->base.base.dev;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	uint32_t aux_ch_mutex, status;
> +	int count = 0;
> +
> +	if (!HAS_AUX_MUTEX(dev))
> +		return false;
> +
> +	/*
> +	 * FIXME: determine actual aux channel
> +	 * Hard coded to channel A for now to protect sink crc requests on eDP.
> +	 */

If you want to leave it like this for now, the please add "|| !is_edp()"
alongside !HAS_AUX_MUTEX() for an early return.

> +	aux_ch_mutex = DP_AUX_MUTEX_A;
> +
> +	if (!get) {
> +		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE | DP_AUX_MUTEX_STATUS);
> +		return false;
> +	}
> +
> +	/*
> +	 * The Bspec specifies waiting 500us between attempts to acquire the
> +	 * mutex.  Ten retries should be adequate to balance successfully
> +	 * acquirng the mutex and spending too much time trying.
> +	 */
> +	while (count++ < 10) {

Please use a for loop whenever you can use a for loop. The reader has to
pause for a second to ensure "while (count++ < 10)" does the right thing
and count is initialized properly; "for (i = 0; i < 10; i++)" comes from
the spine.

> +		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE);
> +		status = I915_READ(aux_ch_mutex);
> +		if (!(status & DP_AUX_MUTEX_STATUS))
> +			return true;
> +		udelay(500);
> +	}

You should probably add an error or a debug message here.

I observe that the caller has no way of knowing whether the lock was not
acquired because the platform doesn't support it, or because we failed
to acquire it. I would imagine the callers might want to opt for not
proceeding to mess with the hardware if they can't ensure exclusive
access. That's kind of the point of locking.

> +
> +	return false;
> +}
> +
> +#define skl_aux_mutex_get(dev) skl_aux_mutex(dev, true)
> +#define skl_aux_mutex_put(dev) skl_aux_mutex(dev, false)

Please have two separate functions instead of this indirection. Name
them _lock and _unlock; _get and _put imply support for
refcounting/nesting, which isn't there.

> +
>  static int
>  intel_dp_aux_ch(struct intel_dp *intel_dp,
>  		const uint8_t *send, int send_bytes,
> @@ -3927,10 +3968,14 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  	u8 buf;
>  	int count, ret;
>  	int attempts = 6;
> +	bool aux_mutex_acquired = false;

Unnecessary initialization.

> +
> +	aux_mutex_acquired = skl_aux_mutex_get(intel_dp);
>  
>  	ret = intel_dp_sink_crc_start(intel_dp);
> +

Unwanted whitespace change.

>  	if (ret)
> -		return ret;
> +		goto release;
>  
>  	do {
>  		intel_wait_for_vblank(dev, intel_crtc->pipe);
> @@ -3957,6 +4002,11 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  
>  stop:
>  	intel_dp_sink_crc_stop(intel_dp);
> +
> +release:
> +	if (aux_mutex_acquired)
> +		aux_mutex_acquired = skl_aux_mutex_put(intel_dp);

No need to do an assignment here.

BR,
Jani.


> +
>  	return ret;
>  }

-- 
Jani Nikula, Intel Open Source Technology Center
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[PATCH] drm/i915/skl: Implement DP Aux Mutex framework

[Wayne Boyer]

From: "Boyer, Wayne" <wayne.boyer@intel.com>

Beginning with SKL the DP Aux channel communication can be protected
using a built in HW mutex.

When PSR is enabled the HW takes control on AUX and uses it to
control panel exit/entry states.

When validating PSR with automated tests, grabbing CRC from sink
revealed strange aux communication issues.  Aux reads were returning
a message read size equal to 0 and 0 is a forbidden message.

By using the HW mutex the HW is blocked from using aux when running
the automated PSR tests.

This patch provides an initial implementation for using that mutex.
The use is currently limited to protecting the sink crc request based
on feedback from the H/W designers indicating that using the mutex
for all aux channel communication is not recommended.

v2: Improved commit message to explain the case where the HW mutex is
helpful.  Also added bug reference.
v3: Fix typos in commit message.

Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91437
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/i915_reg.h |  5 ++++
 drivers/gpu/drm/i915/intel_dp.c | 52 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d5cf30b..ac7ed0d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2585,6 +2585,7 @@ struct drm_i915_cmd_table {
 
 #define HAS_DDI(dev)		(INTEL_INFO(dev)->has_ddi)
 #define HAS_FPGA_DBG_UNCLAIMED(dev)	(INTEL_INFO(dev)->has_fpga_dbg)
+#define HAS_AUX_MUTEX(dev)	(INTEL_INFO(dev)->gen >= 9)
 #define HAS_PSR(dev)		(IS_HASWELL(dev) || IS_BROADWELL(dev) || \
 				 IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev) || \
 				 IS_SKYLAKE(dev) || IS_KABYLAKE(dev))
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 8bd2699..f9ee874 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4288,6 +4288,11 @@ enum skl_disp_power_wells {
 #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
 #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
 
+#define DP_AUX_MUTEX_A			0x6402C
+#define DP_AUX_MUTEX_B			0x6412C
+#define   DP_AUX_MUTEX_ENABLE		    (1 << 31)
+#define   DP_AUX_MUTEX_STATUS		    (1 << 30)
+
 /*
  * Computing GMCH M and N values for the Display Port link
  *
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index da02ed7..b3c7d82 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -781,6 +781,47 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp *intel_dp,
 	       DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
 }
 
+static bool skl_aux_mutex(struct intel_dp *intel_dp, bool get)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_device *dev = intel_dig_port->base.base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t aux_ch_mutex, status;
+	int count = 0;
+
+	if (!HAS_AUX_MUTEX(dev))
+		return false;
+
+	/*
+	 * FIXME: determine actual aux channel
+	 * Hard coded to channel A for now to protect sink crc requests on eDP.
+	 */
+	aux_ch_mutex = DP_AUX_MUTEX_A;
+
+	if (!get) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE | DP_AUX_MUTEX_STATUS);
+		return false;
+	}
+
+	/*
+	 * The Bspec specifies waiting 500us between attempts to acquire the
+	 * mutex.  Ten retries should be adequate to balance successfully
+	 * acquirng the mutex and spending too much time trying.
+	 */
+	while (count++ < 10) {
+		I915_WRITE(aux_ch_mutex, DP_AUX_MUTEX_ENABLE);
+		status = I915_READ(aux_ch_mutex);
+		if (!(status & DP_AUX_MUTEX_STATUS))
+			return true;
+		udelay(500);
+	}
+
+	return false;
+}
+
+#define skl_aux_mutex_get(dev) skl_aux_mutex(dev, true)
+#define skl_aux_mutex_put(dev) skl_aux_mutex(dev, false)
+
 static int
 intel_dp_aux_ch(struct intel_dp *intel_dp,
 		const uint8_t *send, int send_bytes,
@@ -3927,10 +3968,14 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 	u8 buf;
 	int count, ret;
 	int attempts = 6;
+	bool aux_mutex_acquired = false;
+
+	aux_mutex_acquired = skl_aux_mutex_get(intel_dp);
 
 	ret = intel_dp_sink_crc_start(intel_dp);
+
 	if (ret)
-		return ret;
+		goto release;
 
 	do {
 		intel_wait_for_vblank(dev, intel_crtc->pipe);
@@ -3957,6 +4002,11 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 
 stop:
 	intel_dp_sink_crc_stop(intel_dp);
+
+release:
+	if (aux_mutex_acquired)
+		aux_mutex_acquired = skl_aux_mutex_put(intel_dp);
+
 	return ret;
 }
 
-- 
1.9.1

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